<div id="checkbox">
    <select v-model="selected" @change='func()'>
        <option value='' disabled selected style='display:none;'>选择1</option>
        <option v-for="option in options" v-bind:value="option.value">
            {{ option.text }}
        </option>
    </select>
    <select name="" id="">
        <option value='' disabled selected style='display:none;'>选择2</option>
        <option v-for="option in options2" v-bind:value="option.text">
            {{ option.text }}
        </option>
    </select>
</div>
<script type="text/javascript" src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
<script>
    new Vue({
        el: '#checkbox',
        data: {
            selected: '',
            options: [ //一级菜单
                {
                    text: 'A',
                    value: 'A'
                },
                {
                    text: 'B',
                    value: 'B'
                },
                {
                    text: 'C',
                    value: 'C'
                }
            ],
            options2: [], //二级菜单
        },
        methods: {
            func: function () { //绑定事件，给二级菜单赋值
                switch (this.selected) {
                    case 'A':
                        this.options2 = [{
                            text: 'A-1'
                        }, {
                            text: 'A-2'
                        }, {
                            text: 'A-3'
                        }];
                        break;
                    case 'B':
                        this.options2 = [{
                            text: 'B-1'
                        }, {
                            text: 'B-2'
                        }, {
                            text: 'B-3'
                        }];
                        break;
                    case 'C':
                        this.options2 = [{
                            text: 'C-1'
                        }, {
                            text: 'C-2'
                        }, {
                            text: 'C-3'
                        }];
                        break;
                }
            }
        }
    })
</script>